1. Field of the Invention
The present invention relates to a liquid ejection apparatus and a liquid maintenance method, and more particularly, to a liquid ejection apparatus which ejects liquid toward a prescribed medium and a liquid maintenance method which maintains the state of the liquid.
2. Description of the Related Art
There is a liquid ejection apparatus which ejects dispersion liquid in which dispersed micro-particles are suspended. Examples of material of the micro-particles include, for instance, pigment, high-polymer resin, metal, glass, or oxide or compound of these. Generally, the micro-particles tend to aggregate and settle with the passage of time. When the liquid in which the micro-particles have aggregated and settled is ejected, then there is deterioration of quality in the ejection results, namely, density non-uniformities or distortions, poor color reproduction, non-uniform density of the micro-particles, and the like. Therefore, technology for maintaining the state of the dispersion liquid has been proposed.
For example, Japanese Patent Application Publication No. 2004-167698 discloses a liquid ejection apparatus in which a liquid ejection head having a projection on the bottom is supported on a carriage, which moves reciprocally in a main scanning direction, and a cam is provided to press the projection of the liquid ejection head to move the liquid ejection head in a substantially perpendicular direction (a vertical direction) with respect to the carriage so that the liquid ejection head to perform a swinging motion in the substantially perpendicular direction (the vertical direction) and the liquid inside a liquid chamber (ink cartridge) held on the liquid ejection head is agitated in such a manner that a settled state of the contents in the liquid is eliminated.
Japanese Patent Application Publication No. 2004-216809 discloses technology in which, when nozzles of an inkjet head oppose a recording medium (i.e., in a printing state), a free surface of the ink (the liquid-atmosphere interface, which is also commonly called “meniscus”) in the nozzle that is not to eject the ink is caused to vibrate to an extent in which the ink is not ejected, while the ink is ejected and discarded through the nozzles when not printing.
Japanese Patent Application Publication No. 2003-72104 discloses technology in which a manifold guiding ejection material (e.g., ink) to a nozzle of a liquid ejection head is provided with a piezoelectric element for agitating the ejection material inside the manifold. By continuously agitating the ejection material inside the manifold by means of the piezoelectric element, the ejection material immediately prior to ejection is maintained in a state of stable dispersion of micro-particles.
However, in some cases, it is difficult to achieve efficient agitation of liquid in which dispersed micro-particles are suspended.
In particular, in a liquid ejection apparatus having a liquid ejection head in which the liquid ejection face is situated in a bottommost position, nozzle blockages are liable to occur due to sedimented micro-particles in the nozzles. In the case of a so-called shuttle head structure in which the liquid ejection head performs a reciprocal back and forth movement, the liquid inside the liquid ejection head is agitated by the reciprocal motion of the liquid ejection head, but in the case of a line head structure where the liquid ejection head does not perform reciprocal movement, the liquid is not agitated usually.
As described above, technology has been proposed for carrying out various maintenance operations, such as the vertical swinging of the liquid ejection head, the slight vibration of the free surface of the ink in the nozzle, the discarding of the ink, and the like; however, these operations are difficult to apply in practice, since they are not efficient because of long waiting times, increased costs, and so on.
For example, in Japanese Patent Application Publication No. 2004-167698, the liquid ejection head is caused to swing in the substantially vertical direction by means of the cam pressing the projection arranged on the bottom of the liquid ejection head; however, the liquid ejection head performs no reciprocal back and forth movement. The liquid having the aggregated and settled micro-particles in the liquid cartridge is thus agitated only by the displacement of the liquid ejection head in the substantially perpendicular direction, and hence the agitation performance is low and a long time is required until the liquid is agitated to a satisfactory extent.
In Japanese Patent Application Publication No. 2004-216809, since valuable liquid is ejected and discarded when the apparatus is not in printing, there is a problem in that costs increase.
In Japanese Patent Application Publication No. 2003-72104, since the dispersed state of the micro-particles is maintained by continuously agitating the liquid by means of the piezoelectric element, then it is not effective unless the piezoelectric element continuously carries out the agitating operation even while the apparatus is not operating, and it results in high power consumption and increased costs.
Furthermore, if a structure is adopted in which a common liquid chamber is arranged at a position higher than pressure chambers and the base of the common liquid chamber is connected to the pressure chambers through liquid supply channels, then the high-density liquid nearby the base of the common liquid chamber in which the micro-particles have settled is supplied to the pressure chambers, and hence there is a progressive density change (from thick to thin) in the liquid as being consumed by ejection. Consequently, quality deterioration occurs in the ejection results.